The Antarctic ozone hole — one of the deepest, largest gap in the ozone layer in the last 40 years — has closed, according to the World Meteorological Organization (WMO).

Try this PYQ:

Q.Consider the following statements:

Chlorofluorocarbons, known as ozone-depleting substances are used:

1. In the production of plastic foams
2. In the production of tubeless tyres
3. In cleaning certain electronic components
4. As pressurizing agents in aerosol cans

Which of the statements given above is/are correct?

(a) 1, 2 and 3 only

(b) 4 only

(c) 1, 3 and 4 only

(d) 1, 2, 3 and 4

Antarctic Ozone Hole

• The Antarctic “ozone hole” was discovered by British Antarctic Survey scientists Farman, Gardiner and Shanklin in 1985.
• It came as a shock to the scientific community because the observed decline in polar ozone was far larger than anyone had anticipated.
• It was caused by the chemical reactions on polar stratospheric clouds (PSCs) in the cold Antarctic stratosphere caused a massive.
• Though localized and seasonal, an increase in the amount of chlorine present in active, ozone-destroying forms.

Role of PSCs

• The polar stratospheric clouds in Antarctica are only formed when there are very low temperatures, as low as −80 °C, and early spring conditions.
• In such conditions, the ice crystals of the cloud provide a suitable surface for the conversion of unreactive chlorine compounds into reactive chlorine compounds, which can deplete ozone easily.

An annual process

• An ozone hole is the thinning of the ozone layer boosted in size by colder temperatures.
• The formation of the ozone hole in the Antarctic has been an annual occurrence and has been recorded for the last 40 years.
• Human-made chemicals migrate into the stratosphere and accumulate inside the polar vortex. It begins to shrink in size as warmer temperatures dominate.
• As the temperatures high up in the stratosphere start to rise, ozone depletion slows, the polar vortex weakens and breaks down.
• By the end of December, ozone levels return to normal.

The hole closes after achieving peak

• The annually occurring ozone hole over the Antarctic had rapidly grown from mid-August and peaked at around 24 million square kilometres — one of the largest so far — in early October 2020.
• The expansion of the hole was driven by a strong, stable and cold polar vortex and very cold temperatures in the stratosphere.
• The same meteorological factors also contributed to the record 2020 Arctic ozone hole, which has also closed.

Note: A polar vortex is a wide expanse of swirling cold air, a low-pressure area, in Polar Regions. During winters, the polar vortex at the North Pole expands, sending cold air southward.

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